1. Field of the Invention
This invention relates to a zoom lens, and more particularly, to a wide-angle zoom lens of a projector for projecting images.
2. Description of Related Art
Demands for a projector for displaying images on a large-dimension screen have increased in both the family domain and business domain. Since the displaying angles of the projectors currently available in the market are not wide enough, that is, the focal lengths of those projectors are too long, a longer distance between a zoom lens and the screen is needed for displaying an image on a large-dimension screen. Therefore, in a case that a liquid crystal display (LCD) panel, which has a fixed dimension, is used as an object, displaying images on a large-dimension screen cannot be accomplished by using those zoom lenses available today.
As referring to Table 1, the listed zoom lenses from different manufacturers, such as NEC, Toshiba, Philip, Sanyo, and Panasonic, are not able to display images on a large-dimension screen within a limited space, wherein the displayed object is a 1.3-inch LCD panel. In Table 1, column 3, column 4, column 5, and column 6 represent the f-number of the projection system (FNO), focal length for wide-mode position (EFL1, in millimeter), focal length for tele-mode (EFL2, in millimeter), and projection distance (L, in meter) of each zoom lens, respectively. The adjustable focal point of the 1.3-inch LCD panel varies from about 47.5 mm to 52.5 mm. In the case of displaying an image on a large-dimension screen, a 200-inch screen for example, the shortest distance needed for the zoom lens of model number PLC-8800 from Sanyo is 7.37 m at the widest projecting angle of 47.6 mm. For most middle size conference rooms, the foregoing required conditions for displaying an image on a large-dimension screen normally cannot be fulfilled.
TABLE 1 ______________________________________ Manufacturer Model Number FNO EFL1 EFL2 L ______________________________________ NEC MULTISYNC MT1000 2.5.about. 52 73 8.05 Toshiba TLP-511 2.5.about.3.0 50 70 7.74 Philip PROSCREEN 4600 2.9.about.3.5 50 75 7.74 Sanyo PLC-8800 2.5.about.3.5 47.6 76.2 7.37 Panasonic PT-L390E 3.2.about.3.5 53.5 76.4 8.28 ______________________________________
According to the foregoing, a conventional zoom lens, which requires a long distance between the zoom lens and the display screen, is not suitable for most regular-size conference rooms.